Volatile chemicals used by insects for communication, known as semiochemicals, have been used for a number of years in the control of insect pests in agriculture. The use of semiochemicals for insect control offers a number of significant advantages over the use of chemical insecticides. Semiochemicals generally exhibit little toxicity toward humans and other nontarget organisms. Due to their volatility and instability caused by oxidation and photochemical degradation, they do not persist in the environment or leave detectable residues on treated crops.
It is known that many species of aphid communicate distress of various kinds by releasing a particular semiochemical known as an alarm pheromone. The principal constituent of the alarm pheromone for many of these aphids is the compound E-.beta.-farnesene (EBF). Other lesser constituents of the alarm pheromone include the related farnesene isomers Z-.beta.-, E-E-, E-Z-, Z-Z , and Z-E-.alpha.-farnesenes. Studies of the behavior of aphids in the presence of vapors of EBF have shown that the typical aphid alarm symptoms include cessation of sucking and 25 dispersal away from the source of the pheromone. Wientjens et al., 29 Experientia 658 (1973). U.S. Pat. No. 4,505,934 discloses that 10 wt % solutions of EBF exhibit contact insecticidal action when applied topically to aphids. European patent application No. 0 266 822 discloses the use of EBF as an aphid control at concentrations exceeding that which causes the alarm reaction (1 to 10 ng/ml), teaching that concentrations exceeding 10 ng/ml cause a hormonal reaction that results in delayed or interrupted development of aphids and other insects. The principal drawback of both of these prior art uses of EBF is that both require relatively large amounts of the pheromone, which is very expensive.
What is needed, therefore, is an effective way to utilize EBF as an aphid control at relatively low concentrations. This need and others are met by the present invention, which is summarized and described in detail below.